Substrate assembly, method of forming the same, and electronic device including the same

ABSTRACT

A substrate assembly includes a first hexagonal boron nitride sheet directly bonded to a surface of a substrate, and a metal layer on the first hexagonal boron nitride sheet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.10-2013-0030982, filed on Mar. 22, 2013, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND

1. Field

Some example embodiments relate to a substrate assembly, a method offorming the same, and/or an electronic device including the same. Thesubstrate assembly, which includes a hexagonal boron nitride sheet,which is directly bonded to a surface of the substrate for use and themethod of forming the substrate assembly do not need an additionaltransfer process. Thus, by directly bonding the hexagonal boron nitridesheet to the surface of the substrate, defects on the substrate assemblymay be minimized, and the number of layers of the hexagonal boronnitride sheet may be easily adjusted.

2. Description of the Related Art

Hexagonal boron nitride is a material which has a two-dimensional (2D)structure. The hexagonal boron nitride is formed in a hexagonalarrangement of a boron atom and a nitrogen atom. The hexagonal boronnitride has electrical insulating characteristics due to a large bandgapof about 5.9 eV, and is physically and mechanically stable.

As a crystal of the hexagonal boron nitride has a hexagonal stackedstructure, similarly to graphite, the crystal of the hexagonal boronnitride forms a very strong bonding and has lubrication. Additionally,the hexagonal boron nitride is a covalently bonding element with a lowatomic number and has a high conduction quality. The hexagonal boronnitride sublimates at a temperature of about 3,000° C. without a meltingpoint. Thus, the hexagonal boron nitride has high stability at a hightemperature. The hexagonal boron nitride has a very high electricresistance, and has a resistance of 105Ω in a high temperature area. Asthe hexagonal boron nitride has highly stable hexagonal bonding, thehexagonal boron nitride has a high chemical stability. A true specificgravity of the hexagonal boron nitride, which is 2.28, is very low,compared to other ceramics. Thus, the weight of components used in anaircraft and a space material, may be made lighter.

As one of the methods of manufacturing the hexagonal boron nitride, anelectronic device may be manufactured by growing the hexagonal boronnitride through a process of supplying boron and nitrogen sources to ametal catalyst and performing a heat treatment on the metal catalyst,and then, separating and transferring the hexagonal boron nitride to agiven (or alternatively, predetermined) substrate. However, damage onthe hexagonal boron nitride, such as tears or wrinkling defects, may beunintentionally generated in the transferring process. Furthermore, athickness or the number of layers of a hexagonal boron nitride sheet maynot be easily adjusted by controlling the amounts of the boron andnitrogen sources.

Accordingly, a substrate assembly, in which the hexagonal boron nitridesheet is directly bonded to a surface of the substrate and in which athickness or the number of layers of the hexagonal boron nitride sheetmay be easily controlled, and a method of forming the same are needed.

SUMMARY

Some example embodiments provide a substrate assembly which includes afirst hexagonal boron nitride sheet that is directly bonded to a surfaceof a substrate.

Other example embodiments also provide a method of forming a substrateassembly which includes a first hexagonal boron nitride sheet directlybonded to a surface of a substrate.

Other example embodiments also provide an electronic device whichincludes the substrate assembly.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of example embodiments.

According to an example embodiment, a substrate assembly includes asubstrate, a first hexagonal boron nitride sheet directly bonded to asurface of the substrate, and a metal layer on the first hexagonal boronnitride sheet.

The first hexagonal boron nitride sheet may not have wrinkling defectsin a region that amounts to 90% or more of an area of the substrate. Thefirst hexagonal boron nitride sheet may include 1 to 100 layers. Boronnitride may constitute 95% or more per 1 mm² area of the first hexagonalboron nitride sheet. The metal layer may include a catalyst layer formedof one of at least one metal and an alloy thereof, the metal includingone of nickel (Ni), cobalt (Co), iron (Fe), platinum (Pt), palladium(Pd), gold (Au), aluminum (Al), chrome (Cr), copper (Cu), magnesium(Mg), manganese (Mn), molybdenum (Mo), rhodium (Rh), silicon (Si),thallium (Ta), titanium (Ti), tungsten (W), uranium (U), vanadium (V),and zirconium (Zr).

A grain of the metal layer may have an average area of 1 μm² to1,000,000 μm². The substrate assembly may further include a second firsthexagonal boron nitride sheet on the metal layer. The substrate mayinclude at least one of a metal or semimetal oxide-based substrate, asilica-based substrate, a boron nitride-based substrate, and asilicon-based substrate.

According to another example embodiment, a method of forming a substrateassembly includes preparing a substrate in a chamber, combining asolid-state nitrogen source and a boron source on the substrate, forminga metal layer on a surface of the substrate including the solid-statenitrogen and boron sources, and forming a first hexagonal boron nitridesheet directly bonded to the surface of the substrate by performing aheat treatment on the substrate including the solid-state nitrogensource, the boron source and the metal layer.

At least one of ammonia borane (H₃NBH₃), borazine ((BH)₃(NH)₃), andpolyborazylene may be combined on the substrate. The method may furtherinclude dissolving the solid-state nitrogen and boron sources in anorganic solvent in a concentration range from 1 mM to 10M prior to thecombining. The first hexagonal boron nitride sheet may be formed bysimultaneously performing the heat treatment on the substrate andexposing the substrate to one of an inert gas, a hydrogen gas, and amixture of an inert gas and a hydrogen gas. The heat treatment may beperformed for 1 to 20 hours at a temperature of 100° C. to 2,000° C.

According to yet another example embodiment, a method of forming asubstrate assembly includes preparing a substrate in a chamber, forminga metal layer on the substrate, and forming a first hexagonal boronnitride sheet between the substrate and the metal layer, the firsthexagonal boron nitride sheet being directly bonded to a surface of thesubstrate. The first hexagonal boron nitride sheet is formed by applyingat least one of a nitrogen source and a boron source in one of a gas andsolid state to the substrate from outside the metal layer, andperforming a heat treatment on the substrate.

The method may further include forming a second hexagonal boron nitridesheet prior to or simultaneously with the forming a first hexagonalboron nitride sheet. The heat treatment may be performed at atemperature of 100° C. to 2000° C. under one of an inert gas, a hydrogengas, and a mixture of an inert gas and a hydrogen gas. A gas-statenitrogen source including at least one of NH₃ and N₂, and a gas-stateboron source including at least one of BH₃, BF₃, BCl₃, B₂H₆, (CH₃CH₂)₃B,(CH₃)₃B, and diborane may be applied to the substrate from outside themetal layer. A solid-state boron source including B₂O₃ may be applied tothe substrate from outside the metal layer. At least one of H₃NBH₃,(BH)₃(NH)₃, and polyborazylene may be applied to the substrate fromoutside the metal layer.

According to yet another example embodiment, an electronic deviceincludes the substrate assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1A is an atomic force microscopy (AFM) image of a first hexagonalboron nitride sheet included in a substrate assembly of Example 2;

FIG. 1B is an AFM image of a second hexagonal boron nitride sheetincluded in the substrate assembly of Example 2;

FIG. 2 is an optical surface image of a nickel layer included in thesubstrate assembly of Example 2;

FIG. 3A is a transmission electron microscope (TEM) image of the firsthexagonal boron nitride sheet included in the substrate assembly ofExample 2;

FIG. 3B is a TEM image of the second hexagonal boron nitride sheetincluded in the substrate assembly of Example 2;

FIG. 4A is a TEM image of a first hexagonal boron nitride sheet includedin the substrate assembly of Example 3;

FIG. 4B is a TEM image of a second hexagonal boron nitride sheetincluded in the substrate assembly of Example 3;

FIG. 5A is a TEM image of a first hexagonal boron nitride sheet includedin the substrate assembly of Example 4;

FIG. 5B is a TEM image of a second hexagonal boron nitride sheetincluded in the substrate assembly of Example 4;

FIG. 6A is a TEM image of a first hexagonal boron nitride sheet includedin the substrate assembly of Example 5;

FIG. 6B is a TEM image of a second hexagonal boron nitride sheetincluded in the substrate assembly of Example 5;

FIG. 7A is a Raman spectrum of the first and second hexagonal boronnitride sheets included in the substrate assembly of Example 2 by usingan Ar+ ion laser with a wavelength of 514 nm;

FIG. 7B is a Raman spectrum of the second hexagonal boron nitride sheetincluded in the substrate assembly of Example 2 by using an Ar+ ionlaser with a wavelength of 514 nm;

FIG. 8A is a schematic diagram illustrating the substrate assembly ofExample 1;

FIG. 8B is a schematic diagram illustrating the substrate assembly ofExample 2; and

FIG. 9 is an X-ray photoelectron spectroscopy (XPS) depth profile graphobtained by analyzing a depth of the first and second hexagonal boronnitride sheets included in the substrate assembly of Example 2 by usingan XPS surface analyzing apparatus.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain aspects of the present description.

Hereinafter, a substrate assembly, a method of forming the same, and anelectronic device including the same, according to some exampleembodiments, will be described in detail. However, the description isonly an example, and the scope of the inventive concepts is defined notby the detailed description but by the appended claims.

FIG. 8A is a schematic diagram illustrating a substrate assembly 40 ofan example embodiment, i.e. Example 1. FIG. 8B is a schematic diagramillustrating a substrate assembly 500 of another example embodiment,i.e. Example 2.

The substrate assembly 40, 500 includes a substrate 10, 100; a firsthexagonal boron nitride sheet 20, 200 formed on the substrate 10, 100;and a metal layer 30, 300 formed on the first hexagonal boron nitridesheet 20, 200. The first hexagonal boron nitride sheet 20, 200 may bebonded directly to a surface of the substrate 10, 100.

In the description, “bonded directly to a surface of the substrate 10,100” refers to chemically and/or physically bonding directly to asurface of the substrate 10, 100, and to a first hexagonal boron nitridesheet which is grown in-situ on the surface of the substrate 10, 100.Thus, unlike a hexagonal boron nitride sheet which is formed on anadditional substrate, a strong bonding force between the substrate 10,100 and the first hexagonal boron nitride sheet 20, 200 may be obtained.The first hexagonal boron nitride sheet 20, 200, which is bondeddirectly to the surface of the substrate 10, 100, may be identified fromTEM images which are shown in FIGS. 3A, 4A, 5A, and 6A, a Raman spectrumwhich is obtained by using an Ar⁺ ion laser with a wavelength of 514 nm,and an X-ray photoelectron spectroscopy (XPS) depth profile graph whichis shown in FIG. 9.

The first hexagonal boron nitride sheet 20, 200 may not includewrinkling defects in a region that amounts to 90% or more of an area ofthe substrate 10, 100. For example, the first hexagonal boron nitridesheet 20, 200 may not include wrinkling defects in a region that amountsto 93% or more of an area of the substrate 10, 100. This may beconfirmed from the number of wrinkling defects per each unit area in anatomic force microscopy (AFM) image shown in FIG. 1A, which is describedlater.

The first hexagonal boron nitride sheet 20, 200 may be formed of 1 layerto 90 layers, for example, 1 to 90 layers or 1 to 80 layers. The numberof layers of the first hexagonal boron nitride sheet 20, 200 may beadjusted depending on a purpose of an electronic device that ultimatelyuses the layers. The number of layers of the first hexagonal boronnitride sheet 20, 200 may be confirmed from transmission electronmicroscope (TEM) images shown in FIGS. 3A, 4A, 5A, and 6A, which aredescribed later.

Boron nitride may make up 95% or more per 1 mm² area of the firsthexagonal boron nitride sheet 20, 200. For example, boron nitride maymake up 99% or more per 1 mm² area of the first hexagonal boron nitridesheet 20, 200. With such a proportion of boron nitride in the firsthexagonal boron nitride sheet 20, 200, the first hexagonal boron nitridesheet 20, 200 may be kept homogeneous. Thus, the electroniccharacteristics of an electronic device which employs the firsthexagonal boron nitride sheet 20, 200 may be kept uniform.

The first hexagonal boron nitride sheet 20, 200 may be formed bypenetrating of a nitrogen source, a boron source, or nitrogen and boronsources in a gas or solid state which is or are located outside themetal layer 30, 300, via an inside of the metal layer 30, 300 which isformed of a plurality of grain boundaries and its or their diffusing(s)on the substrate 10, 100.

The metal layer 30, 300 has a polycrystalline structure. Thus, the metallayer 30, 300 includes a plurality of grains, which are partitioned by agrain boundary. The first hexagonal boron nitride sheet 20, 200 may beformed by passing of a nitrogen source, a boron source, or nitrogen andboron sources in a gas or solid state which is or are located outsidethe metal layer 30, 300 into the metal layer 30, 300, via a plurality ofthe grain boundaries partitioning the plurality of grains, and its ortheir diffusing(s) on the substrate 10, 100.

In the description, “outside the metal layer 30, 300” refers to an areawhich is located on, upper, below, or at a side of the metal layer 30,300, except inside the metal layer 30, 300.

The gas-state nitrogen source may be at least one selected from amongNH₃ and N₂, and the gas-state boron source may be at least one selectedfrom among BH₃, BF₃, BCl₃, B₂H₆, (CH₃CH₂)₃B, (CH₃)₃B, and diborane. Thesolid-state boron source may include B₂O₃. The solid-state nitrogen andboron sources may be at least one selected from among ammonia borane(H₃NBH₃), borazine (BH)₃(NH)₃, and polyborazylene.

The metal layer 30, 300 may be a catalyst layer formed of at least onemetal or an alloy thereof which is selected from the group consisting ofnickel (Ni), cobalt (Co), iron (Fe), platinum (Pt), palladium (Pd), gold(Au), aluminum (Al), chrome (Cr), copper (Cu), magnesium (Mg), manganese(Mn), molybdenum (Mo), rhodium (Rh), silicon (Si), thallium (Ta),titanium (Ti), tungsten (W), uranium (U), vanadium (V), and zirconium(Zr). For example, the metal layer 30, 300 may be a catalyst layer whichis formed of at least one metal or an alloy thereof, selected from thegroup consisting of Ni, Fe, Mo, and Cu.

A grain of the metal layer 30, 300 may have an average area of, forexample, 1 μm² to 1000,000 μm². For example, a grain of the metal layer30, 300 may have an average area of 1 μm² to 80,000 μm².

An average area of a grain is obtained by using an arithmetic average ofan area of each unit grain, instead of a total area of all grainsincluded in the metal layer 30, 300. For example, an average area of thegrain may be obtained by visually measuring the number of grains in acertain area, which is provided in an optical image of a surface of anickel layer shown in FIG. 2 which is described later, for example, inan area of 1 cm×1 cm, and then, dividing the certain area by the numberof the grains.

Such an average area of the grain may be increased by using a heattreatment process in a chamber at a high temperature of about 500° C., aphysical polishing process, a chemical polishing process, a chemicalmechanical polishing process, or an electrolytic polishing processwithin a range of the average area described above. However, an averagearea of the grain may not exceed 1,000,000 μm² so that a nitrogensource, a boron source, or nitrogen and boron sources, in a gas or solidstate, which is or are located outside the metal layer 30, 300, may passthrough the metal layer 30, 300.

The second hexagonal boron nitride sheet 400 may further be included onthe metal layer 30, 300 formed on the first hexagonal boron nitridesheet 20, 200. The second hexagonal boron nitride sheet 400 may beformed by applying a nitrogen source, a boron source, or nitrogen andboron sources, in a gas or solid state, is or are applied to the metallayer 30, 300.

The second hexagonal boron nitride sheet 400 may be formed of 1 to 100layers, for example, 1 to 90 layers or 1 to 80 layers. The number oflayers of the second hexagonal boron nitride sheet 400 may be adjustedwithin a range of the layers described above depending on a purpose ofan electronic device that uses the layers. The number of layers of thesecond hexagonal boron nitride sheet 400 may be confirmed from TEMimages shown in FIGS. 3B, 4B, 5B, and 6B which are described later.

The second hexagonal boron nitride sheet 400 may not include wrinklingdefects in a region that amounts to 70% or more of an area of thesubstrate 10, 100. For example, the second hexagonal boron nitride sheet400 may not include wrinkling defects in a region that amounts to 70% ormore of an area of the substrate 10, 100. This may be confirmed from thenumber of wrinkling defects per each unit area in an AFM image shown inFIG. 1B which is described later. That is, the number of wrinklingdefects included in the second hexagonal boron nitride sheet 400 ishigher than the number of wrinkling defects in the first hexagonal boronnitride sheet 20, 200. This is because the metal layer 30, 300, on whichthe second hexagonal boron nitride sheet 400 is formed, may be expandedby heat treatment and may be influenced by air. On the contrary, thesubstrate 10, 100, on which the first hexagonal boron nitride sheet 20,200 is formed, may not be influenced by air, but may be expanded by heattreatment. Additionally, the expansion of the substrate 10, 100 by heattreatment is comparatively less than the expansion of the metal layer30, 300 by heat treatment at a high temperature.

The substrate 10, 100 may be at least one selected from among a metal orsemimetal oxide-based substrate, a silica-based substrate, a boronnitride-based substrate, and a silicon-based substrate. For example, themetal or semimetal oxide-based substrate may be Al₂O₃, sapphire,titanium oxide (TiO₂), zinc oxide (ZnO), zirconium dioxide (ZrO₂),hafnium oxide (HfO₂), magnesium oxide (MgO) nickel oxide (NiO), cobalt(II) oxide (Co₂O), copper (II) oxide (CuO), iron oxide (FeO), orSiO_(x), where 0<x≦2. The silica-based substrate may be SiO₂, glass, orquartz. The substrate 10, 100 may have a thickness of, for example,about 1 mm to about 10 mm.

According to another example embodiment, a method of forming a substrateassembly includes preparing a substrate in a chamber; combining solidstate nitrogen and boron sources on the substrate; forming a metal layeron a surface of the substrate on which the solid-state nitrogen andboron sources are combined; and forming a first hexagonal boron nitridesheet, which is directly bonded to the surface of the substrate byperforming a heat treatment on the substrate on which the solid-statenitrogen and boron sources are combined and the metal layer is formed.

A type and thickness of the substrate is as described above. Forexample, a metal or semimetal oxide-based substrate, such as SiO_(x),where 0<x≦2 may be used.

The solid-state nitrogen and boron sources may be at least one selectedfrom among H₃NBH₃, (BH)₃(NH)₃, and polyborazylene. For example, thesolid-state nitrogen and boron sources may be H₃NBH₃. The method ofcombining solid_state nitrogen and boron sources on the substrate mayinclude a process of applying a polymer, such as polyborazylene, to thesubstrate, or a process of forming H₃NBH₃ or (BH)₃(NH)₃ on the substrateby using a coating method, such as spin coating or bar coating.

A solution, in which the solid-state nitrogen and boron sources aredissolved in an organic solvent in a concentration range from about 1 mMto about 10M, may be employed as the solid-state nitrogen and boronsources. For example, a solution, in which solid-state nitrogen andboron are dissolved in an organic solvent in a concentration range fromabout 10 mM to about 1M, may be employed. The organic solvent may varywith a type of the solid-state nitrogen and boron sources. Examples ofthe organic solvent may include tetrahydrofuran (THF),N,N-dimethylformamide (DMF), N-methylpyrrolidine, and isopropanol (IPA).

The heat treatment may be performed under an inert gas, a hydrogen gas,or a mixture of an inert gas and a hydrogen gas, so as to prevent orinhibit oxidation of the nitrogen and boron sources. An argon gas and ahydrogen gas may be used as the inert gas. If the mixture of an inertgas and a hydrogen gas is used, the inert gas may make up about 60 toabout 90 volume percent of a total volume of the chamber, and thehydrogen gas may make up about 5 to about 40 volume percent of a totalvolume of the chamber. The heat treatment may be performed for about 1to about 20 hours at a temperature of about 100° C. to about 2000° C.The heat treatment may be performed at a heating rate of 10° C./min to100° C./min at a range of the temperature described above. The source ofthe heat treatment can use induction heating, radiant heat, laser,infrared rays (IR), microwaves, plasma, ultraviolet (UV) rays, orsurface plasmon heating, but non-limiting sources may be used.

Damage on the substrate may be prevented or inhibited, and volatilityfrom the metal layer and the first hexagonal boron nitride sheet may beprevented or inhibited, due to the supply of the solid-state nitrogenand boron sources in the above-described concentration range and theperformance of the heat treatment in the above-described range of thetemperature and the hours. As such, the first hexagonal boron nitridesheet, which includes 1 to 100 layers, may be formed. In order to obtainthe first hexagonal boron nitride sheet, which includes 1 to 100 layers,the heat-treatment may be maintained, for example, for about 0.001 toabout 1,000 hours, or about 10 seconds to 1 hour.

After the heat treatment, a cooling process may further be performed.The cooling process is a process in which the first hexagonal boronnitride sheet is uniformly grown so as to be regularly arranged. Forexample, the first hexagonal boron nitride sheet may be cooled at a rateof 10° C. to 100° C. per minute. Additionally, the first hexagonal boronnitride sheet may be cooled by applying an inert gas, such as a nitrogengas, at a certain flow rate or by using a natural cooling method.

The metal layer may be formed by using a metal coating method, such as achemical deposition method, a physical deposition method, a sputteringmethod, or an atomic layer deposition (ALD) method. However, a method offorming the metal layer is not limited thereto.

According to another example embodiment, a method of forming a substrateassembly includes preparing a substrate in a chamber; forming a metallayer on the substrate; and forming a first hexagonal boron nitridesheet, which is directly bonded to the substrate, between the substrateand the metal layer by applying a nitrogen source, a boron source, ornitrogen and boron sources in a gas or solid state from outside of themetal layer to the substrate, and then performing a heat treatment onthe substrate.

The first hexagonal boron nitride sheet may be formed by penetrating ofa nitrogen source, a boron source, or nitrogen and boron sources in agas or solid state, which is or are applied from outside the metallayer, into an inside of the metal layer, which is formed of a pluralityof grain boundaries and its or their diffusing(s) on the substrate.

The method may further include forming the second hexagonal boronnitride sheet, before or simultaneously with the forming of the firsthexagonal boron nitride sheet.

In the case that the first and second hexagonal boron nitride sheets aresimultaneously formed, both the first and second hexagonal boron nitridesheets have the same shape. Additionally, as a concentration of thenitrogen source, the boron source, or the nitrogen and boron sources,which is or are in a gas or solid state and applied from outside themetal layer, increases, an increasing amount of the nitrogen source, theboron source, or the nitrogen and boron sources penetrates through theinside of the metal layer that is formed of the plurality of grainboundaries.

The heat treatment may be performed at a temperature of about 100 toabout 2000° C. for about 1 to about 20 hours under an inert gas, ahydrogen gas, or a mixture of an inert gas and a hydrogen gas. After theheat treatment, a cooling process may be further performed. An argon gasand a helium gas may be used as the inert gas. If the mixture of aninert gas and a hydrogen gas is used, the inert gas may make up about 60to about 90 volume percent of a total volume of the chamber, and thehydrogen gas may make up about 5 to about 40 volume percent of a totalvolume of the chamber.

The heat treatment can be performed by using induction heating, radiantheat, laser, IR, microwaves, plasma, UV rays, or surface plasmon heatingas a heat source. The heat treatment may be performed at a heating rateof 100° C./min to 10° C./min within a range of the temperature describedabove. If the heating treatment is performed within a range of thetemperature and the hours, damages on the substrate may be prevented orinhibited, and volatility from the metal layer, the first hexagonalboron nitride sheet, and the second hexagonal boron nitride sheet may beprevented or inhibited. Additionally, the first hexagonal boron nitridesheet, which includes 1 to 100 layers, and the second hexagonal boronnitride sheet, which includes fewer layers than the first hexagonalboron nitride sheet, may be obtained.

The heat treatment for obtaining the first hexagonal boron nitridesheet, which includes 1 to 100 layers, and the second hexagonal boronnitride sheet, which includes fewer layers than the first hexagonalboron nitride sheet, may be maintained, for example, for about 0.001 toabout 1,000 hours, or about 10 seconds to about 1 hour.

After the heat treatment, a cooling process may be further performed.The cooling process may be performed so that the formed first hexagonalboron nitride sheet may be uniformly grown, and thus, may be regularlyarranged. For example, the first hexagonal boron nitride sheet may becooled at a rate of about 10° C. to about 100° C. per minute. Otherwise,the first hexagonal boron nitride sheet may be cooled by using a naturalcooling method.

The gas-state nitrogen source may be at least one selected from amongNH₃ and N₂. The gas-state boron source may be at least one selected fromthe group consisting of BH₃, BF₃, BCl₃, B₂H₆, (CH₃CH₂)₃B, (CH₃)₃B, anddiborane. The solid-state boron source may include B₂O₃. The gas-stateor solid-state nitrogen and boron sources may be at least one selectedfrom among H₃NBH₃, (BH)₃(NH)₃, and polyborazylene. For example, thesolid-state boron source or the solid-state nitrogen and boron sourcesis or are stored in an external container, and boiled at a given (oralternatively, predetermined) temperature. Then, the compound, which isthe solid-state boron source or the solid-state nitrogen and boronsources, is vaporized or sublimated, and then supplied to a chamber inwhich the metal layer is placed. A nitrogen gas may be supplied to thechamber, together with solid-state boron source or the solid-statenitrogen and boron sources.

A solution, in which the solid-state nitrogen and boron are dissolved inan organic solvent in a concentration range from about 1 mM to about10M, may be employed as the solid-state nitrogen and boron sources. Forexample, a solution, in which solid-state nitrogen and boron aredissolved in an organic solvent in a concentration range from about 10mM to about 1M, may be employed. The organic solvent may vary with atype of the solid-state nitrogen and boron sources. Examples of theorganic solvent may include THF, N,N-dimethylformamide (DMF),N-methylpyrrolidine, and isopropanol (IPA).

The metal layer may be a catalyst layer formed of at least one metal oran alloy thereof, selected from the group consisting of Ni, Co, Fe, Pt,Pd, Au, Al, Cr, Cu, Mg, Mn, Mo, Rh, Si, Ta, Ti, W, U, V, and Zr. Forexample, the metal layer may be a catalyst layer formed of at least onemetal or alloy thereof, selected from the group consisting of Ni, Fe,Mo, and Cu. The metal layer may be formed by using a metal coatingmethod, such as a chemical deposition method, a physical depositionmethod, a sputtering method, or an ALD method, but a method ofprocessing the metal layer is not limited thereto.

A type and thickness of the substrate is as described above. Forexample, a metal-based or semimetal oxide-based substrate, such asSiO_(x), where 0<x≦2, may be used.

Additionally, after forming the substrate assembly by using the method,a method of removing the metal layer may be further performed. A processof using an acid may be performed as the method of removing the metallayer. A given (or alternatively, predetermined) concentration ofhydrochloric acid, sulfuric acid, nitric acid, or a mixture thereof maybe used for the acidification process. The substrate assembly may bedipped into the hydrochloric acid, the sulfuric acid, the nitric acid,or the mixture thereof for a given (or alternatively, predetermined)time.

According to another example embodiment, an electronic device includesthe substrate assembly described above. The substrate assembly may beeffectively used in various display devices, such as a field-emissiondisplay (FED), a liquid crystal display (LCD), and an organiclight-emitting diode (OLED) display; and electronic devices, such asvarious batteries like a supercapacitor, a fuel cell, and a solar cell,various nanodevices, such as a field-effect transistor (FET) and amemory device, electronic devices, such as a hydrogen storage element,an optical fiber, and a sensor. As the substrate assembly includes thefirst hexagonal boron nitride sheet that is directly bonded to a surfaceof the assembly, an additional transfer process is not necessary. Thus,when the substrate assembly is used in the electronic device, damages onthe first hexagonal boron nitride sheet may be minimized.

A size of the substrate may be freely adjusted. Thus, the firsthexagonal boron nitride sheet may have a large size, with a laterallength and/or a longitudinal length of about 1 mm or more, for example,about 10 mm or more, or about 10 mm to 1,000 m.

Hereinafter, the inventive concepts will be described in detail, byreferring to embodiments. However, the inventive concepts are notlimited thereto.

Example 1

A 3 cm×3 cm silicon substrate, which is coated with SiO₂ to a thicknessof 100 nm, is prepared. An ultrasonic process is performed on thesubstrate by alternately using water, ethanol, and acetone. Then, thesubstrate is washed and dried.

0.647M of an ammonia borane solution, obtained by dissolving 0.02 g ofH₃NBH₃ in 1 mL of THF, is prepared. In an argon atmosphere reactionchamber, 300 μl of the ammonia borane solution is drop-casted on thesubstrate. Then, the silicon substrate is spin-coated at 1000 rpm forone minute. Nickel is deposited on a surface of the spin-coated siliconsubstrate by using e-beam evaporation. Thus, a nickel layer with athickness of 300 nm is formed.

The silicon substrate is located in a chemical vapor deposition (CVD)chamber. A mixture of 20 volume percent argon and 80 volume percent H₂is applied to the CVD chamber at a flow rate of 100 scfm, by using aninductive heating source, a temperature in the CVD chamber rises to1000° C. for 1.5 hours at a rate of 10° C. per minute, and the CVDchamber is maintained for an hour at the temperature of 1000° C. Then,the inductive heating source is removed, and the CVD chamber is cooledto room temperature at a rate of 10° C. per minute. Thus, a firsthexagonal boron nitride sheet, which is directly bonded to a surface ofthe substrate, is formed.

Example 2

Nickel is deposited on a 3 cm×3 cm silicon substrate, which is coatedwith SiO₂ to a thickness of 100 nm, by using e-beam evaporation. Thus, anickel layer with a thickness of 300 nm is formed on the siliconsubstrate. An ultrasonic process is performed on the silicon substrateby alternately using water, ethanol, and acetone. Then, the substrate iswashed and dried.

0.647M of an ammonia borane solution, obtained by dissolving 0.02 g ofH₃NBH₃ in 1 mL of THF, is prepared. In an argon atmosphere reactionchamber, 300 μl of the ammonia borane solution is drop-casted on thesilicon substrate. Then, the silicon substrate is spin-coated at 1000rpm for one minute.

The silicon substrate is located in a CVD chamber. A mixture of 20volume percent argon and 80 volume percent H₂ is applied to the CVDchamber at a flow rate of 100 scfm, and by using an inductive heatingsource, a heat treatment is performed on the CVD chamber. Thus, atemperature in the CVD chamber rises to 1000° C. for 3 hours at a rateof 100° C. per minute. The CVD chamber is maintained for an hour at thetemperature of 1000° C. Then, the inductive heating source is removed,and the CVD chamber is cooled to room temperature at a rate of 20° C.per minute. Thus, a 47-layer first hexagonal boron nitride sheet, whichis directly bonded to a surface of the substrate, and an 8-layer secondhexagonal boron nitride sheet, on the nickel layer, are formed.

Example 3

Nickel is deposited on a 3 cm×3 cm silicon substrate, which is coatedwith SiO₂ to a thickness of 100 nm, by using e-beam evaporation. Thus, anickel layer with a thickness of 300 nm is formed on the siliconsubstrate. An ultrasonic process is performed on the silicon substrateby alternately using water, ethanol, and acetone. Then, the substrate iswashed and dried.

0.9720M of an ammonia borane solution, obtained by dissolving 0.03 g ofH₃NBH₃ in 1 mL of THF, is prepared. In an argon atmosphere reactionchamber, 300 μl of the ammonia borane solution is drop-casted on thesilicon substrate. Then, the silicon substrate is spin-coated at 5000rpm for one minute.

The silicon substrate is located in a CVD chamber. A mixture of 20volume percent argon and 80 volume percent H₂ is applied to the CVDchamber at a flow rate of 100 scfm, and by using an inductive heatingsource, a heat treatment is performed on the CVD chamber. Thus, atemperature in the CVD chamber rises to 1000° C. for 3 hours at a rateof 100° C. per minute. The CVD chamber is maintained for an hour at thetemperature of 1000° C. Then, the inductive heating source is removed,and the CVD chamber is cooled to room temperature at a rate of 20° C.per minute. Thus, a 67-layer first hexagonal boron nitride sheet, whichis directly bonded to a surface of the substrate, and a 10-layer secondhexagonal boron nitride sheet, on the nickel layer, are formed.

Example 4

Nickel is deposited on a 3 cm×3 cm silicon substrate, which is coatedwith SiO₂ to a thickness of 100 nm, by using e-beam evaporation. Thus, anickel layer with a thickness of 300 nm is formed on the siliconsubstrate. An ultrasonic process is performed on the silicon substrateby alternately using water, ethanol, and acetone. Then, the substrate iswashed and dried.

1.29M of an ammonia borane solution, obtained by dissolving 0.04 g ofH₃NBH₃ in 1 mL of THF, is prepared. In an argon atmosphere reactionchamber, 300 μl of the ammonia borane solution is drop-casted on thesilicon substrate. Then, the silicon substrate is spin-coated at 5000rpm for one minute.

The silicon substrate is located in a CVD chamber. A mixture of 20volume percent argon and 80 volume percent H₂ is applied to the CVDchamber at a flow rate of 100 scfm, and by using an inductive heatingsource, a heat treatment is performed on the CVD chamber. Thus, atemperature in the CVD chamber rises to 1000° C. for 3 hours at a rateof 100° C. per minute. The CVD chamber is maintained for an hour at thetemperature of 1000° C. Then, the inductive heating source is removed,and the CVD chamber is cooled to room temperature at a rate of 20° C.per minute. Thus, a 60-layer first hexagonal boron nitride sheet, whichis directly bonded to a surface of the substrate, and a 29-layer secondhexagonal boron nitride sheet, on the nickel layer, are formed.

Example 5

Nickel is deposited on a 3 cm×3 cm silicon substrate, which is coatedwith SiO₂ to a thickness of 100 nm, by using e-beam evaporation. Thus, anickel layer with a thickness of 300 nm is formed on the siliconsubstrate. An ultrasonic process is performed on the silicon substrateby alternately using water, ethanol, and acetone. Then, the substrate iswashed and dried.

The silicon substrate is located in a CVD chamber. A mixture of 20volume percent argon and 80 volume percent H₂ is applied to the CVDchamber at a flow rate of 100 scfm, and by using an inductive heatingsource, a temperature in the CVD chamber rises at a rate of 100° C. perminute. While the temperature in the CVD chamber reaches 400° C., 100 mgof (BH)₃(NH)₃ is applied to the CVD chamber. After the CVD chamber ismaintained at 400° C. for 30 minutes, the CVD chamber is heat-treatedfor 2 hours, so as to reach a temperature of 1000° C. Then, theinductive heating source is removed, and the CVD chamber is cooled toroom temperature at a rate of 20° C. per minute. Thus, a 62-layer firsthexagonal boron nitride sheet, which is directly bonded to a surface ofthe substrate, and a 44-layer second hexagonal boron nitride sheet, onthe nickel layer, are formed.

Experimental Example 1 An AFM (Atomic Force Microscopy) Image of aHexagonal Boron Nitride Sheet

FIGS. 1A and 1B illustrate AFM images of the first and second hexagonalboron nitride sheets, which are formed in the substrate assembly ofExample 2.

FIGS. 1A and 1B respectively show an optical image of which a total areais covered with the first hexagonal boron nitride sheet and the secondhexagonal boron nitride sheet, which have a total area of 50×60 um²,without a vacant space.

A result of analyzing the first hexagonal boron nitride sheet,manufactured by the Example 2, shows that the first hexagonal boronnitride sheet, which includes a relatively uniform surface, is formed.The first hexagonal boron nitride sheet may not include wrinklingdefects in a region that amounts to 90% or more of a total area of thesubstrate. Whereas, the second hexagonal boron nitride sheet may notinclude wrinkling defects in a region that amounts to 70% or more of atotal area of the substrate.

Additionally, a result of analyzing the total area of the firsthexagonal boron nitride sheet, by dividing the total area in units of0.01 mm², shows that 95% or more per 1 mm² area per 1 mm² is coveredwith boron nitride.

Experimental Example 2 An Optical Surface Image of the Metal Layer

FIG. 2 illustrates an optical surface image of the nickel layer whichhas a total area of 250×200 um² and formed on the 4-inch substrateassembly of Example 2.

As illustrated in FIG. 2, the nickel layer, which is formed on thesubstrate of Example 2, is mainly formed of grains with a size of about150 μm. Referring to FIG. 2, grains of the nickel layer, formed in thesubstrate assembly of Example 2, have an area of about 70,650 μm².

Experimental Example 3 A TEM Image

A TEM image, in which a cross section of the first and second hexagonalboron nitride sheets that are formed in the substrate assembly ofExamples 2 through 5 is measured, is respectively illustrated in FIGS.3A, 3B, 4A, 4B, 5A, 5B, 6A, and 6B.

As illustrated in FIGS. 3A, 3B, 4A, 4B, 5A, 5B, 6A, and 6B, the firsthexagonal boron nitride sheet, formed on the substrate of Examples 2through 5 is directly bonded to a surface of the substrate, and thesecond hexagonal boron nitride sheet is formed on the metal layer.

The first hexagonal boron nitride sheet is respectively formed of 47layers, 67 layers, 60 layers, and 62 layers on the substrate assembly ofExamples 2 through 5. The second hexagonal boron nitride sheet isrespectively formed of 8 layers, 10 layers, 29 layers, and 44 layers onthe nickel layer.

Experimental Example 4 Raman Spectrum

A Raman spectrum of the first and second hexagonal boron nitride sheets,which are formed in the substrate assembly of Example 2, is measured byusing an Ar⁺ ion laser with a wavelength of 514 nm. A result ofmeasuring the Raman spectrum is shown in FIGS. 7A and 7B.

As shown in FIGS. 7A and 7B, the formation of a hexagonal boron nitridesheet may be identified from a peak near 1368 cm⁻¹ to 1370 cm⁻¹. Thepeak near 1368 cm⁻¹ to 1370 cm⁻¹ may be identified when observed at anypoint in the AFM images shown in FIGS. 1A and 1B.

Experimental Example 5 An X-Ray Photoelectron Spectroscopy (XPS) DepthProfile

A depth profile of the substrate assembly of Example 2, is analyzed byusing an XPS, which is Physical Electronics QUANTUM 2000. The result ofthe analyzing is shown in FIG. 9.

As illustrated in FIG. 9, the first hexagonal boron nitride sheet isformed to be directly bonded to a surface of the substrate, and thesecond hexagonal boron nitride sheet is formed on the nickel layer.

As described above, according to the one or more of the above exampleembodiments, the substrate assembly, which includes a hexagonal boronnitride sheet, which is directly bonded to a surface of the substrate,and the method of forming the substrate assembly do not need anadditional transfer process. Thus, defects on the substrate assembly maybe minimized or reduced, and the number of layers of the hexagonal boronnitride sheet may be more easily adjusted.

It should be understood that the example embodiments described thereinshould be considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments.

What is claimed is:
 1. A substrate assembly comprising: a substrate; afirst hexagonal boron nitride sheet directly bonded to a surface of thesubstrate; and a metal layer on the first hexagonal boron nitride sheet;wherein the first hexagonal boron nitride sheet is a sheet which isgrown in-situ on the surface of the substrate, and the first hexagonalboron nitride sheet does not have wrinkling defects in a region thatamounts to 90% or more of an area of the substrate.
 2. The substrateassembly of claim 1, wherein the first hexagonal boron nitride sheetincludes 1 to 100 layers.
 3. The substrate assembly of claim 1, whereinboron nitride constitutes 95% or more per 1 mm² area of the firsthexagonal boron nitride sheet.
 4. The substrate assembly of claim 1,wherein the metal layer includes a catalyst layer formed of at least onemetal or an alloy thereof, the metal including one of nickel (Ni),cobalt (Co), iron (Fe), platinum (Pt), palladium (Pd), gold (Au),aluminum (Al), chrome (Cr), copper (Cu), magnesium (Mg), manganese (Mn),molybdenum (Mo), rhodium (Rh), silicon (Si), thallium (Ta), titanium(Ti), tungsten (W), uranium (U), vanadium (V), and zirconium (Zr). 5.The substrate assembly of claim 1, wherein a grain of the metal layerhas an average area of 1 μm² to 1,000,000 μm².
 6. The substrate assemblyof claim 1, further comprising: a second first hexagonal boron nitridesheet on the metal layer.
 7. The substrate assembly of claim 1, whereinthe substrate includes at least one of a metal or semimetal oxide-basedsubstrate, a silica-based substrate, a boron nitride-based substrate,and a silicon-based substrate.
 8. An electronic device comprising thesubstrate assembly of claim 1.